1. Field of the Invention
The present invention relates to an object detecting device for detecting an object by transmitting an electromagnetic wave comprising a laser or a millimeter wave to the object and receiving the reflected wave thereof.
2. Description of the Related Art
FIG. 14 shows a prior art object detecting device for detecting the distance from a vehicle to another vehicle T traveling ahead of the vehicle (which will be referred to as a preceding vehicle) and the direction of the preceding vehicle. The prior art object detecting device is designed to detect the distance and direction of the preceding vehicle T by vertically and laterally scanning with an electromagnetic wave transmitted forwards from a radar device provided at a front portion of the vehicle V and receiving the wave reflected by the preceding vehicle T.
In the above prior art device, the electromagnetic wave transmitted forwards from the radar device is diffused radiantly. For this reason, the width of the area for detecting the preceding vehicle T is narrower at a location closer to the vehicle V and wider at a location farther from the vehicle V. For example, in an object detecting device having a maximum detecting distance of 100 m, if the width of an area equal to 0.8 m which is approximately one-half of the lateral width of the preceding vehicle T, is ensured at a location 100 m ahead of the vehicle V, the width of the area is as small as 0.08 m at a location 10 m ahead of the vehicle V and hence, the reflected wave cannot be received with the preceding vehicle defined as a lump of object. For this reason, when distance from the vehicle V to the preceding vehicle T is farther, the preceding vehicle T can be detected. However, when the distance becomes short, only the reflected wave from a portion of a vehicle body of the preceding vehicle T is received. If the reflection state of the electromagnetic wave reflected from such portion of the vehicle body is bad, there is a possibility that the preceding vehicle could not be detected.